Described below is a piezoelectric component with outer contacting, having gas phase deposition. In addition a method for manufacturing the component and use of the component are disclosed.
Piezoelectric components are typically used in the automotive industry for control of fuel injection valves. At the heart of these components is a piezoelement in which an electrode layer and the further electrode layer are arranged above one another. Located between the electrode layers is a piezoelectric layer. The piezoelectric layer typically is formed of a piezoceramic with lead-zirconate titanate (PZT). By activating the electrode layers with different electrical potentials an electric field is coupled into the piezoelectric layer. As a result of the coupled-in electric field there is a deflection (expansion or contraction respectively) of the piezoelectric layer and thereby of the piezoelement.
To achieve the greatest possible deflection while at the same time transmitting the highest possible force, the piezoelectric components are designed as multilayer components. In such cases a plurality of piezoelements are arranged above one another to form a piezoelement stack. Arranged alternately above one another in the piezoelement stack are electrode layers (inner electrodes) and piezoelectric layers.
Usually a so-called multilayer capacitor structure is realized for contacting the electrode layers. In such cases the electrode layers are routed alternately to different lateral surfaces of the piezoelement and thereby to different lateral surfaces of the piezoelement stack and electrically contacted there. In the case of monolithic piezoelement stacks in particular the problem here is that the electrode layers do not delimit the full surface of the piezoelectric layer arranged between them. The non-full-surface arrangement leads to piezoelectrically-active and piezoelectrically-inactive areas. Different electric fields are coupled into these areas. As a result of the different electric fields different deflections are produced and thereby mechanical stresses. These mechanical stresses generally lead to tears. The tears can be tolerated per se. However they lead to a significant outlay in respect of an outer electrode attached to the side surface of the piezoelement stack for electrical contacting of the electrode layers.
An alternate variant to this is represented by the so-called fully-active piezoactuator. In this piezoactuator the electrode layers and the further electrode layers delimit of the full surfaces of the piezoelectric layers arranged between them. This means that an essentially equal electrical field is coupled into the entire piezoelectric layer. The result is that mechanical stresses and resulting tears hardly occur. However the requirement for this is that the electrode layers are able to the individually electrically controlled. It must be ensured that the electrode layers can have the corresponding electrical potentials applied to them independently of each other.
It has already been proposed, for electrical contacting of the electrode layers up to the side surface of the piezoelement stack to first apply an insulation layer. Subsequently the insulation layer is selectively opened. Applied through the openings is an outer contacting with metallic particles having a particle diameter of 5 μm to 20 μm.